Metal coated film

ABSTRACT

There is described a multi-layer oriented polyolefin film suitable for receiving a metal layer to form a high barrier thereon the film comprising a coat polymer layer at one surface, an metallizable polymer layer at the opposite surface and a core polymer layer sandwiched between and separating the coat layer and the metallizable layer where (a) the metallizable layer comprises at least one metallocene polypropylene (mPP); and/or (b) the core layer comprises at least 2% by weight (preferably at least 10%) of a hard resin preferably selected from at least one of: a dicyclopentadiene (DCPD) resin; a propylene-butylene copolymer and/or a hydrocarbon resin obtainable from C5 and/or C9 monomer(s). Preferably the film of the invention is metallized on at least one outer surface, more preferably directly onto the metallizable layer containing mPP.

The present invention relates to polymericfilms which are suitable forreceiving a metal coat thereon and such films so metallised, as well asmethods of preparing these films.

Polymeric films are often provided with a metal coat thereon as this isboth aesthetically pleasing and also imparts a very high barrier to thefilm for gas and water transmission. It would be desirable to providefilms which have an improved adhesion to such metal coatings so that thecoating is substantially free of blemishes thereon and provides betterbarrier properties.

It is also desirable that such films are printable and heat sealable.

Certain films prepared from metallocene polypropylene (mPP) with a lowmolecular weight hydrocarbon resin (hard resin) are described in U.S.Pat. No. 6,165,599 (Demeuse). This document describes the type ofmetallocene catalysts that may be used to make mPP as used herein aswell as described some of the hard resins that may also be used herein.The contents of this document are hereby incorporated by reference.

However Demeuse does not suggest that mPP and/or hard resin may beincorporated into BOPP multi-layer metallised films of the particularstructure described herein in order to provide metal coated films havingimproved properties. Instead Demeuse teaches that these non-metallisedfilms have improved optical properties. Demeuse neither suggests thatthe mPP coat be added to a surface layer to add metallisation nor thatthe hard resin in a core layer may also provide metallised films withimproved properties.

Therefore broadly in accordance with the present invention there isprovided a multi-layer oriented polyolefin film suitable for receiving ametal layer to form a high barrier thereon the film comprising a coatpolymer layer at one surface, an metallisable polymer layer at theopposite surface and a core polymer layer sandwiched between andseparating the coat layer and the metallisable layer characterised inthat

-   -   (a) the metallisable layer comprises at least one metallocene        polypropylene (mPP); and/or    -   (b) the core layer comprises at least 2% (preferably at least        10%) by weight of a hard resin.

Further aspects of the present invention provide for a film of theinvention as described above coated with a metal coat on themetallisable layer and also a method of making such a metallised filmcomprising the step of coating a metallisable film as describe hereinwith metal coat on the metallisable layer.

Metallocene catalysts may comprise bridged bisdicyclopentadienyl orbisindenyl Group 4,5 or 6 transition metal dihalide derivatives.Specific metallocene catalysts known to be useful for producingpolypropylene (mPP) are described in EP 0485820; EP 0485821, EP 0485822;EP 0485823, EP 0518092, EP 0519237, U.S. Pat. No. 5,145,819 and U.S.Pat. No. 5,296,434. Other references that discuss the metallocenecatalysed process include EP 351,932, U.S. Pat. No. 5,055,438 U.S. PatNo. 5,234,800; U.S. Pat. No. 5,272,016; U.S. Pat. No. 5,272,236 and U.S.Pat No. 5,278,272. All of the cited documents are incorporated herein byreference.

Conveniently the hard resins incorporated in the core layer of the filmsof the present invention comprise a low molecular weight hydrocarbonresins which may be hydrogenated or unhydrogenated resins derived fromolefin monomers. Examples of such resins comprise those derived fromterpene monomers, coal tar fractions and petroleum feedstocks. Suitableresins include those prepared from terpene monomers (e.g., limonene,alpha and beta pinene, such as Piccolyte resins from HerculesIncorporated, Wilmington, Del., and Zonatac resins from Arizona ChemicalCompany, Panama City, Fla.). Other low molecular weight resins areprepared from hydrocarbon monomers and mixtures thereof, such as C₅monomers (e.g., piperylene, cyclopentene, cyclopentadiene, andisoprene), oligomerized C₅ monomers, particularly the thermallyoligomerized C_(0.5) monomers such as the hydrogenated thermallyoligomerized cyclopentadiene resins sold under the trade name Escorez(for example Escorez 5300) by Exxon Chemical Co. of Baytown, Tex. Othersare prepared from C₉ monomers, particularly the monomers derived fromC_(0.9) petroleum fractions which are mixtures of aromatics, includingstyrene, methyl styrene, alpha methyl styrene, vinyl naphthalene, theindenes and methyl indenes and, additionally, pure aromatic monomers,including styrene, .alpha.-methyl-styrene and vinyltoluene. Examples ofthese resins include hydrogenated .alpha.-methyl styrene-vinyl tolueneresins sold under the trade name Regalrez by Hercules Incorporated ofWilmington, Del. The hydrogenated C₉ and pure monomer resins arepreferred. Particularly preferred are the hydrogenated cyclopentadieneresins and the hydrogenated aromatic resins derived from pure aromaticmonomers, e.g., the hydrogenated.alpha.-methyl styrene-vinyltoluenecopolymers.

More preferred hard resins are selected from at least one of: adicyclopentadiene (DCPD) resin; a propylene-butylene copolymer and/or ahydrocarbon resin obtainable from C₅ and/or C₉ monomer(s).

Preferably the film of the invention is metallised on at least one outersurface more, more preferably directly on the metallisable layer whichoptionally may first be conventionally treated by any suitable means(e.g. by corona discharge).

Without wishing to be bound by any mechanism it is believed that theimproved barrier properties of metallised films of the invention arisebecause of the smooth surface for metallisation resulting from the useas the metallisable layer the highly regularly crystalline mPP.Alternatively or as well it is believed the addition of hard resin tothe core layer increases the barrier of that layer to penetrationtherethrough should any species be able to penetrate any imperfections(pin hole defects etc) in the metal surface coat.

Further aspects and preferred features of the invention are given in theclaims.

The invention will now be illustrated by reference to the followingnon-limiting examples

All the films described herein were made as follows.

A three layer polymeric tube was formed by coextruding through anannular nozzle three polymer streams, a core layer A of polypropylene(referred to herein as PP) homopolymer; an outer layer B of one coatpolymer on the outside of the tube; and an inner layer C of another coatpolymer on inside of the tube. The extruded tube so formed comprises athree layer film with layers A B C from the outer to inner surface. Thetube was cooled and subsequently re-heated before being blown into abubble to orient the film. A film web was obtained (without collapsingthe bubble onto itself) to form as the resultant film an un-laminatedthree layer biaxially oriented PP (BOPP) film having a layer structure AB C i.e. where there is a coat layer A at one surface of the BOPP film(corresponding to the outside of the bubble) and a metallisable layer Cat the other film surface (corresponding to the inside of the bubble)with a core polymer layer B sandwiched between the these two layers Aand C.

Typically the final film may be about 15 microns thickness on averagewith for example the coat layer “A” being about 0.3 micron thick, thecore layer “B” being about 14 μm thick and the metallisable layer “C”being about 0.6 micron thick.

As used herein the term “metallocene” polypropylene (hereinafter mPP)refers to PP made using a metallocene complex as the polymerisationcatalyst. Such catalysts produce PP in which the tacity of the polymerchain is more readily controlled leading to a more highly orderedpolymer of more regular structure and controlled molecular weight. ThusmPP is more crystalline that conventional PP produced using a ZeigerNata catalyst. It will be appreciated that the mPP used in the inventioncould be substituted with any other PP of similar properties prepared byany other suitable process which is a selective as that for mPP.

For the three layer non-laminate BOPP films tested herein each layer wasconstructed as follows:

Comp I and Comp II—Base Film—Inner and Core Unmodified

Comp I and Comp II were different batches of the same film of:

Coat layer “A” comprises an ethylene-propylene random copolymer with1000 ppm of a conventional silica anti-block agent plus polyformaldehydebeads in polypropylene as an non-migratory slip agent (such as thoseavailable under the trade name ABVT 19) Core layer “B” comprises a PPnucleated homopolymer plus 400 ppm sodium benzoate Metallisable layer“C” was the same as the coat layer “A”

EXAMPLES 1i AND 1ii mPP (Inner)

Examples 1i and 1ii were modified versions of Comp I and II respectivelywhere the metallisable layer “C” comprised a mPP coat polymer plus 1200ppm of a silica anti-block agent.

EXAMPLES 1i AND 1ii mPP (Inner)+Hard Resin (Core)

Examples 2i and 2ii were modified versions of Examples 1i and 1iirespectively where the core layer “B” additionally comprised 10% w/w ofa dicylcopentadiene (DCPD) hard resin

EXAMPLES 3i AND 3ii Modified (Inner)

Examples 3i and 3ii were modified versions of Comp I and II respectivelywhere the metallisable layer “C” comprised a propylene-butylene randomcopolymer plus 1000 ppm of a silica anti-block agent.

EXAMPLES 4i AND 4ii Modified (Inner)+Hard Resin (Core)

Examples 4i and 4ii were modified versions of Examples 3i and 3iirespectively where the core layer “B” additionally comprised 10% w/w ofa dicylcopentadiene (DCPD) hard resin

Film Sample Testing

All samples tested in the evaluation were approximately 30 microns inthickness.

Results Barrier and optical property testing on un-metallised film WVTRSample 38° C./90% RH OTR 23° C./0% RH (%) g/m²/24 hours cm³/m²/24 hoursNAH (%) WAH Comp I 5.2 1975 0-2 1.4 Comp II 5.2 1873 0-3 2.1 Ex 1i 5.61919 0-3 1.6 Ex 1ii 5.9 1782 0-2 1.5 Ex 2i 3.2 861 0-3 1.9 Ex 2ii 3.4894 0-2 2.4 Ex 3i — — — — Ex 3ii — — — — Ex 4i 3.4 933 1-3 1.3 Ex 4ii3.3 618 0-3 1.5

Adhesion to the discharged treated (metallisable) film surface - layer CPrint Adhesion Metal adhesion Sample DT (% pull off) DT (% pull off)Comp I 0% 0% Comp II 0% 0% Ex 1i 0% 0% Ex 1ii 0% 0% Ex 2i 0% 0% Ex 2ii0% 0% Ex 3i — — Ex 3ii — — Ex 4i 0% 0% Ex 4ii 0% 0%

The lower the % pull off the better the print/metal adhesion. Mechanicalproperty testing Sample YM MD YM TD TS MD TS TD EAB MD EAB TD Comp I1856 2853 150 194 101.8 64.6 Comp II 2283 2675 161 180 112.4 65.6 Ex 1i— — — — — — Ex 1ii — — — — — — Ex 2i 3462 3734 139 189  95.2 69.5 Ex 2ii3076 3424 165 192 121.8 75.4 Ex 3i — — — — — — Ex 3ii — — — — — — Ex 4i2366 3689 141 208 108.7 71.2 Ex 4ii 3753 3633 162 203 122.9 68.6YM = Young's modulus (MPa)TS = Tensile strength (MPa)EAB = Elongation at break (%)

Coefficient of friction analysis of examples at 23° C. Sample In/InIn/Out Out/Out In/Metal Out/Metal Comp I Static 0.54 0.45 0.44 0.43 0.35Comp I Dynamic 0.42 0.41 0.38 0.38 0.31 Comp II - Static 0.75 0.60 0.520.52 0.32 Comp II - Dynamic 0.56 0.50 0.44 0.35 0.27 Ex 1i - Static 0.270.29 0.32 0.15 0.14 Ex 1ii - Dynamic 0.22 0.23 0.24 0.13 0.12 EX 2i -Static 0.34 0.30 0.28 0.22 0.16 Ex 2ii - Dynamic 0.29 0.25 0.20 0.160.11 Ex 3i - Static 0.54 0.53 0.45 0.37 0.39 Ex 3ii - Dynamic 0.49 0.440.42 0.33 0.38 Ex 4i - Static 0.52 0.51 0.43 0.32 0.22 Ex 4ii - Dynamic0.42 0.40 0.38 0.23 0.19

Slip properties of the film having a Metallocene polypropylene polymeras the metallisable layer C (Examples 1 and 2) with or without hardresin in the core polymer—layer B—are much lower than the values forbase film Comp I and II. Slip properties of the propylene-butylenemetallisable grade polymer as layer C with hard resin in the corepolymer layer B (Example 4) are similar to the values for base film CompI and II.

Metallised Sample Properties.

Metallised film barrier properties have been compared with a standardbase film Comp I and II.

and a film grade using propylene-butylene copolymer on the coronatreated metallisable side of the film=layer C (Examples 3 and 4). SamplePrint Adhesion WVTR at 38° C./90% RH OTR at 23° C./ 0% RH DT (% pulloff) g/m²/24 hours cm³/m²/24 hours Comp I 5% 0.81 88 Comp II 0% 0.98 136Ex 1i 0% 0.79 43 Ex 1ii 0% 0.46 51 Ex 2i 0% 0.33 32 Ex 2ii 0% 0.43 31 Ex3i 0% 0.32 35 Ex 3ii 0% 0.36 68 Ex 4i 0% 0.31 36 Ex 4ii 5% 0.34 30Conclusions

The results presented above have shown that using metallocenepolypropylene as the metallisable layer C with hard resin in the corepolymer (layer B) gives beneficial effects over metallisation onto thesurface of a conventional BOPP film having a conventional coat polymerlayer. The water vapour and oxygen barrier properties both decrease withthe new polymer as layer C with no print adhesion loss. The hard resinused as the core polymer additive (in layer B) is preferably of thedicyclopentadiene (DCPD) type.

Oxygen and water vapour barrier properties are improved with metallocenepolypropylene as the metallisable surface (layer C) and opticalproperties are similar when metallocene polypropylene is used as layerC. The metallocene polypropylene does not affect printability or metaladhesion on the corona treated surface.

When using the propylene-butylene coat polymer as layer C with hardresin in the core polymer (layer B) similar benefits are seen whencompared to use of metallocene polypropylene as the polymer for layer C.

The use of metallocene polypropylene as a polymer to provide ametallisable film surface gives major benefits with respect to barrierproperties over conventional polymers (such as Zeiger Nata PP) currentlyused to provide metallisable surfaces. Yet optical properties of thefilms of the invention are comparable to those of conventional films.Metallisation of the new film was possible with no detrimental effectson the print adhesion.

The metallocene polypropylene as the metallisable surface (layer C)could be used to produce a very high barrier metallisable film and itcan be seen that the metallised film barrier can be increased evenfurther by the addition of hard resin in the core polymer (layer B).

1. A multi-layer oriented polyolefin film suitable for receiving a metallayer to form a high barrier thereon the film comprising a coat polymerlayer at one surface, a metallizable polymer layer at the oppositesurface and a core polymer layer sandwiched between and separating thecoat layer and the metallizable layer wherein: (a) the metallizablelayer comprises at least one metallocene polypropylene (mPP); and/or (b)the core layer comprises at least 2% by weight of a hard resin.
 2. Themulti-layer film as claimed in claim 1, which comprises both (a) themetallizable layer comprising mPP and (b) the core layer comprising hardresin.
 3. The multi-layer film as claimed in claim 1, in which the corelayer comprises at least 10% by weight of hard resin.
 4. The multi-layerfilm as claimed in claim 1, in which the hard resin is selected from atleast one of: a dicyclopentadiene (DCPD) resin; a propylene-butylenecopolymer and/or a hydrocarbon resin obtainable from C₅ and/or C₉monomer(s).
 5. The multi-layer film as claimed in claim 4, in which thehard resin comprises DCPD.
 6. The multi-layer film as claimed in claim1, which further comprises a metal coat on either surface.
 7. Themulti-layer film as claimed in claim 6, which further comprises a metalcoat applied directly onto the metallizable layer.
 8. The multi-layerfilm as claimed in claim 7, in which the metallizable layer ispretreated to enhanced adhesion of the metal coat before applicationthereof.
 9. The multi-layer film as claimed in claim 8, in which thepre-treatment is a corona discharge.
 10. (canceled)